This invention relates to exposure control systems for photographic cameras, and, more particularly, to a flash photographic exposure control system for a camera having an electrically timed shutter provided with an electronic or mechanical switch by which the camera is switchable from an automatic daylight exposure range to an automatic flash exposure range in response to attainment of a threshold voltage level of a stroboscopic system associated therewith.
For taking photographs with illumination from an activated flash unit, it is necessary to adjust the camera shutter to a predetermined setting such as providing a shutter speed of 1/30 second, or 1/60 second, because of a compromise between a large inertia of the shutter and the output characteristics of the flash unit. Conventionally, this adjustment has been made intentionally by hand, when the camera is used in the flash mode. Therefore, the camera equipped with an automatic daylight exposure range and an automatic flash exposure range has the latent possibilities of improper adjustments of the shutter due to the negligence and erroneous judgment of the camera operator. In such cases, no correct exposure can be made. To resolve this problem, a proposal has been made in which the adjustment of the camera to the particular setting for flash photography is automatically effected in response to attachment of a flash unit to the camera. This arrangement is, however, incapable of responding to the threshold voltage level of the flash unit, permitting the flash tube thereof to be discharged with supply of electrical energy from the main store capacitor even when the main capacitor is charged to a voltage lower than the critical anode-to-cathode voltage of the flash tube, thus resulting in the production of a corresponding improper flash lighting condition.